There have been developed current interruption devices configured to interrupt current to flow between electrode terminals (positive terminal and negative terminal) in case where an electrical energy storage device is overcharged or short-circuiting occurs in the electrical energy storage device. The current interruption device is disposed between the electrode terminal and a corresponding electrode (between positive terminal and positive electrode, or between negative terminal and negative electrode). The current interruption device is configured to interrupt conduction between the electrode terminal and the electrode when pressure in a casing of the electrical energy storage device increases. International Publication No. WO 2013/154166 A1 discloses a current interruption device including a first conductive member connected to the electrode terminal, and a second conductive member connected to the electrode. Hereinafter, International Publication No. WO 2013/154166 A1 is referred to as Patent Literature 1. The first conductive member and the second conductive member are disposed to be spaced from each other. A first deformable member is disposed between the first conductive member and the second conductive member. An end of the first deformable member is connected to the first conductive member, and a center of the first deformable member is connected to the second conductive member. In addition, a second deformable member is disposed on a side opposite to the first deformable member relative to the second conductive member. The second deformable member is provided with a projection. Further, in Patent Literature 1, a first seal member is disposed between the first conductive member and the second conductive member such that an, inside of the current interruption device is kept airtight against an outside of the current interruption device. Still further, a second seal member is disposed between the first conductive member and the casing such that an inside of the casing is kept airtight against an outside of the casing.